1. Field of the Invention
This invention relates to a laser-machining device used for piercing a hole in a workpiece.
2. Description of the Related Art
In a general laser-machining device such as the one disclosed in Japanese Unexamined Patent Publication No. 1-218780, a gap sensor for detecting the distance (hereinafter referred to as “the gap amount”) between the tip of a nozzle for radiating the laser and a workpiece to be machined by laser is arranged in the neighborhood of the tip of the nozzle. When starting to cut the workpiece by the laser-machining device, the nozzle approaches the workpiece based on the gap amount detected by the gap sensor. Then, when the nozzle reaches the desired position, the laser is radiated to pierce a hole, and after piercing a hole, the cutting process is started. In order to maintain the gap amount constant between the tip of the nozzle and the workpiece surface, even during the cutting process, the gap amount is continuously controlled using the gap sensor.
During the piercing process before the cutting process, a plasma may be generated on the surface of the workpiece, so that the gap sensor cannot operate normally, and the operation of the gap control axis may become unstable. In order to avoid this inconvenience, the gap control operation using the gap sensor may be temporarily canceled during the piercing process.
Specifically, in the general laser-machining device described in Japanese Unexamined Patent Publication No. 1-218780, the steps of (1) starting the approach operation of the gap control axis, (2) completing the approach operation, (3) canceling the gap control operation, (4) executing the piercing instruction, (5) resuming the gap control operation, and (6) starting to execute the cutting instruction, are executed in that order. In this way, in the general laser-machining device, the piercing process is executed after the nozzle approaches the position suitable for the piercing process and after completion of the piercing process, the cutting process is started.
In the general laser-machining device disclosed in Japanese Unexamined Patent Publication No. 1-218780, however, the piercing process is executed after the nozzle approach is complete as described above. In other words, with the general laser-machining device, there is the problem that it is required to wait for the completion of nozzle approach and therefore the machining time is increased.
Also, the gap control operation is temporarily canceled during the piercing process. Unless the gap control operation is canceled in this way, the operation of the gap sensor becomes unstable due to the effect of a plasma generated during the piercing process, which in turn makes the gap control operation unstable, thereby making it impossible to execute the piercing process successfully. The gap control operation is canceled to avoid this inconvenience. The cancellation of the gap control operation also consumes some time, and causes an increase in the machining-time.
This invention has been achieved in view of this situation, and the object thereof is to provide a laser-machining device capable of executing the piercing process stably and of reducing the required time.